OK I hope I cover all of this
Ummm check the packaging on the membrane it should say what GPD it is, 50gpd or 75gpd etc? Its all in the membrane as to how much water is produced.
For replacing everything, firstly you should get 0 tds from after the DI, when that lowers, replace the DI as a first thing. Once that is exhausted I plan to replace it again but also replace the prefilters. The membrane is the last thing to replace due to it being the most expensive! Some people just change them every so many months but I think it depends on how you look after the unit.
With the micron Im not 100% sure but I don't think it matters as you have a compact unit, so you will have to buy the sealed pod with the filter in. Just buy the better one.
Sorry missed that there was a flow restrictor already there! OK with my picture the water comes from membrane from the top of the pic, you cant see it but there are arrows on the flow restrictor on mine. The reason it goes as in the pic, basically when the unit is running to make water the ball valve is shut,this causes water to go to the flow restrictor pushing it back to the membrane to get better usage. When you flush the unit to clear anything in there, you need to open the ball valve as it is in the pic, this means water just flows straight through the membrane to flush it all out. How that makes some sense?
So after the flow restrictor the water goes to the drain.
Yes you are right, the good pipe connects to the Di pod,you might need to cut a small piece of your pipe to do this.
With the ball valve put it before the DI pod to lock water in the membrane. Also put one before the flow restrictor and also one before the pipe running into the membrane.
When you are running the unit you run them all on open EXCEPT the one linking around your flow restrictor (my pic) that needs to be shut. Then when not in use close all the ball valves to lock in water.
The ballvalves will connect to pipe, so just cut the pipe where you want it and slide it in
Hope that helps?